1. Field of the Invention
The present invention relates to a process for producing a clear aqueous solution of the magnesium salt of a sulfonic acid type or sulfuric ester type anionic surface active agent. More specifically, it relates to a process for producing a clear or transparent aqueous solution of an anionic surface active agent containing a substantial amount of only slightly water-soluble magnesium salt of alkylbenzene sulfonic acid.
2. Description of the Prior Art
Sulfonic acid type or sulfuric ester type anionic surface active agents have heretobefore been used usually in the form of a sodium salt. However, recently, magnesium salt type anionic surface active agents have become of major interest as an active agent for a detergent having an excellent frothing property.
Generally known methods for producing a sulfonic acid type or sulfuric ester type anionic surface active agent in the form of a magnesium salt are a metathesis or double-decomposition process in which the sodium salt of said anionic surface active agent is reacted with, for example, magnesium chloride and a neutralizing process in which sulfonic acids or sulfuric esters are directly neutrlized with magnesium hydroxide or magnesium oxide. Of these known processes, the former process has a disadvantage that large quantities of inorganic salts are necessarily produced as by-products and must be removed from the product, although the metathesis reaction easily occurs. On the other hand, the latter process has an advantage that such by-product is not formed. However, this process has the disadvantages that, since magnesium oxide or magnesium hydroxide to be used as a neutralizing agent is only slightly soluble in water, a long neutralization operation is required and that a clear neutralization solution cannot be obtained within a generally acceptable time period. Especially, when alkylbenzene sulfonic acid is directly neutralized with magnesium hydroxide, there is only a small chance of obtaining a clear aqueous solution of magnesium alkylbenzene sulfonate.